Phased array antennas (PAAs) allow steering of transmitted Radio Frequency (RF) beam without physically moving the antenna. Phased array antennas are used in an increasing number of applications such as multifunctional radars and communications.
Beamforming is a signal processing technique for adapting the transmission or reception direction of a directional antenna. This can be achieved by feeding different radiation elements of the antenna with phase shifted copies of the same signal. The phase shift values are adjusted so that the radiation elements experience constructive interference in the wanted direction, obtaining a high directivity value.
Moving to the next generation 5G mobile networks, optical beamforming may be used to handle a challenging link budget at higher frequencies, lower emission power levels prescribed by regulation and deployment in densely populated areas.
Beamforming may be achieved by processing electrical signals. At higher frequencies and bandwidths, electrical circuits become more sensitive to oscillator phase noise, phase dependency on the frequency (squint) and signal leakage between adjacent antenna elements.
To mitigate these issues, optical beamforming schemes have been proposed, where the generation of low noise radio frequencies (RF) and accurate phase shift values uses optical devices.
Carrier aggregation is a feature introduced in LTE-Advanced (3GPP Release 10) to increase the mobile connection bandwidth. The frequency selectivity of the radio frequency circuits makes it difficult to combine beamforming and carrier aggregation, especially inter-band carrier aggregation, without the full duplication of the electrical circuits for any frequency to support.